CN112771286A

CN112771286A - Power transmission device

Info

Publication number: CN112771286A
Application number: CN201980063208.9A
Authority: CN
Inventors: 井木泰介; 大场浩量
Original assignee: NTN Corp
Current assignee: NTN Corp
Priority date: 2018-09-28
Filing date: 2019-09-25
Publication date: 2021-05-07
Also published as: EP3859189A4; WO2020067163A1; JP7038637B2; EP3859189A1; JP2020051571A; EP3859189B1

Abstract

A reduction gear (1) is provided with: a plurality of rollers (4); an input member (first member 10) having a plurality of first grooves (13) through which the plurality of rollers (4) pass; a pair of fixing members (second members 5) provided on both sides of the input member (10) in the axial direction and having rolling element engagement grooves (16) in which both ends of the plurality of rollers (4) in the axial direction are engaged; and a pair of output members (third members 31, 32) that are respectively provided between the input member (10) and the pair of fixing members (5) in the axial direction and have a plurality of second grooves (17) through which the plurality of rollers (4) pass. The plurality of first grooves (13) are formed along a circle having a center of curvature eccentric with respect to the rotation center (X). The rolling element engagement groove (16) is formed along a wave-shaped curve that alternately intersects a pitch circle having a center of curvature at the rotation center (X).

Description

Power transmission device

Technical Field

The present invention relates to a power transmission device for transmitting rotation input to an input rotating portion to an output rotating portion coaxially arranged at a predetermined speed ratio.

Background

For example, patent document 1 shows, as shown in fig. 9, a reduction gear device as follows: the input plate 110 having the ball engaging grooves 111 and the output plate 120 having the ball engaging grooves 121 are arranged to face each other in the axial direction, and the rotational torque is transmitted from the input plate 110 to the output plate 120 via the balls 130 engaged in the

ball engaging grooves

111, 121.

Specifically, the reduction gear device includes input plate 110 and output plate 120 provided to be rotatable about a common rotation center X, a plurality of balls 130 interposed between input plate 110 and output plate 120, and a holder 140 fixed to case 160. The first ball engaging groove 111 provided in the input plate 110 is formed in a circular shape, and the second ball engaging groove 121 provided in the output plate 120 is formed in a wave shape (see fig. 10). The input plate 110 is attached to the outer periphery of the input shaft 170 via the eccentric cam 180, and the center of curvature O1 of the circular first ball engagement groove 111 is thereby displaced from the rotation center X by the eccentric amount a. When the input shaft 170 rotates, the input plate 110 revolves around the rotation center X with the wobbling radius a, and accordingly, the balls 130 engaged with the first ball engagement grooves 111 reciprocate in the radial direction in the concave grooves 141 provided in the holder 140. The output plate 120 is rotated by a component force in the rotational direction of the contact force between the balls 130 and the wave-shaped second ball engagement grooves 121.

For example, when the center line O1 of the input plate 110 revolves in the arrow direction from the position shown in fig. 10 in accordance with the rotation of the input shaft 170, the balls 130(a) located above the rotation center X are pressed against the outer diameter side portions of the waveform-shaped second ball engagement grooves 121, and the balls 130(B) located below the rotation center X are pressed against the inner diameter side portions of the waveform-shaped second ball engagement grooves 121. At this time, the output plate 120 is rotated by a component force F (see an arrow) in the rotational direction of the contact force applied from the balls 130 to the second ball-engaging groove 121. In this way, in the above-described speed reducer, not only the balls 130(a) on the upper side of the rotation center X but also the balls 130(B) on the lower side of the rotation center X among the plurality of balls 130 contribute to torque transmission, and therefore, an increase in load capacity and vibration reduction can be achieved.

Documents of the prior art

Patent document

Patent document 1: japanese patent laid-open publication No. 2018-021602

Disclosure of Invention

Problems to be solved by the invention

However, in the above-described speed reduction device, as shown in fig. 11, since the balls 130 are in contact with the respective

ball engagement grooves

111 and 121 at an angle inclined with respect to the axial direction, the contact forces F3 'and F4' (the reaction forces of the contact forces F3 and F4 applied to the balls 130) received by the input plate 110 and the output plate 120 from the balls 130 have radial direction components F3a ', F4 a' and axial direction components F3b 'and F4 b'. Therefore, it is necessary to use bearings capable of receiving loads in both the radial direction and the axial direction for

bearings

151 and 152 supporting input plate 110 and

bearings

153 and 154 supporting output plate 120. As such bearings, deep groove ball bearings and angular contact ball bearings are generally used, but these bearings are less allowed in the axial direction than they are allowed in the radial direction, and therefore if they are selected as bearings capable of withstanding loads in both the radial direction and the axial direction, the bearing size increases, and as a result, the size of the entire reduction gear device increases.

In view of the above, an object of the present invention is to reduce the size of the entire power transmission device that transmits rotational torque in the axial direction via rolling elements.

Means for solving the problems

In order to solve the above problem, the present invention provides a power transmission device for transmitting rotation input to an input rotating portion to an output rotating portion coaxially arranged at a predetermined speed ratio, the power transmission device including: a plurality of rollers; a first member having a plurality of first grooves through which the plurality of rollers pass; a pair of second members provided on both sides of the first member in the axial direction and each having a rolling element engagement groove in which the plurality of rollers are engaged; and a pair of third members provided between the first members and the pair of second members in an axial direction, respectively, and having a plurality of second concave grooves through which the plurality of rollers pass, wherein the plurality of first concave grooves are formed along a circle having a center of curvature eccentric with respect to a center of rotation of the input rotating portion and the output rotating portion, the rolling element engagement grooves are formed along a wavy curve that alternately intersects a pitch circle having a center of curvature at the center of rotation, any one of the first members, the pair of second members, and the pair of third members is provided on the input rotating portion, and the other one of the first members, the pair of second members, and the pair of third members is provided on the output rotating portion.

As described above, in the present invention, a roller (for example, a cylindrical roller) having a cylindrical outer peripheral surface is used as a rolling element for transmitting torque, not a ball. In this case, since almost no axial load is generated between the roller and each member, the bearing that supports the input member and the output member that receive the contact force from the roller is sufficient as a bearing that supports only the radial load. In this way, the load applied to the bearing is limited to the radial direction, so that the bearing can be miniaturized while maintaining durability, and the torque loss in the bearing can be reduced.

However, when a roller is used as the rolling element for transmitting torque as described above, since each member comes into contact with a plurality of axial portions of the outer peripheral surface of the roller and applies contact forces in different directions, a moment may be applied to the roller and the roller may tilt (the center line may be inclined with respect to the axial direction). Therefore, in the present invention, the pair of third members and the pair of second members are disposed symmetrically in the axial direction on both sides in the axial direction of the first member with the first member as the center, and the rollers are inserted into the first concave grooves of the first member and the second concave grooves of the pair of third members, and both ends in the axial direction of each roller are engaged with the rolling element engagement grooves of the pair of second members. Accordingly, since the contact forces applied to the roller from the first concave groove, the second concave groove, and the rolling element engagement groove are axially symmetrical, the moment applied to the roller is cancelled, and the torque can be smoothly transmitted while avoiding the roll from falling.

In the power transmission device, for example, the first member may be provided on the input rotating portion, the pair of third members may be provided on the output rotating portion, and the pair of second members may be used as the fixed members. In this way, by using the second member as the fixing member, the contact force generated between the roller and the second rolling element engagement groove can be maintained by the fixing member, and a large bearing for maintaining the contact force is not required. Further, since only the contact force in the circumferential direction (the rotational direction) is generated between the roller and the second groove of the output and rotating portion by providing the third member in the output and rotating portion, the load applied to the bearing that supports the third member is reduced, the bearing size can be reduced, and the torque loss in the bearing interior can be reduced.

In this case, if the pair of third members provided in the output rotating portion are integrally rotatable, the power that is separately transmitted to both sides in the axial direction from the first member provided in the input rotating portion via the roller can be recombined and output. Further, since the relative position (phase) of the second concave grooves provided in the respective third members is fixed by integrating the pair of third members, the roll can be reliably prevented from falling down by inserting the roll into the second concave grooves.

In the power transmission device, it is preferable that a friction reduction member (for example, a needle bearing or a slide bearing) is provided at a contact portion where the outer peripheral surface of the roller contacts at least one of the three elements of the first recessed groove of the first member, the second recessed grooves of the pair of third members, and the rolling element engagement grooves of the pair of second members. As described above, by bringing the roller into contact with each element via the friction reducing member, the friction loss at the contact portion can be significantly reduced as compared with the case where the roller is brought into direct contact with each element, and therefore the torque transmission efficiency can be further improved.

Effects of the invention

As described above, by using the roller as the rolling element for transmitting the rotational torque in the axial direction, the bearing for supporting the input rotating portion and the output rotating portion can be downsized, the entire device can be downsized, and the torque loss in the bearing can be reduced to improve the torque transmission efficiency. Further, by arranging the pair of second members and the pair of third members axially symmetrically on both sides of the first member in the axial direction, the roll can be prevented from falling down, and the torque can be transmitted efficiently.

Drawings

Fig. 1 is a sectional view of a reduction gear according to an embodiment of the present invention.

Fig. 2 is a front view of the input member (first member).

Fig. 3 is a front view of the fixing member (second member).

Fig. 4 is a front view of the output member (third member).

Fig. 5 is an enlarged view of a V portion of fig. 4.

Fig. 6 is an exploded perspective view schematically showing the input member, the output member, the fixing member, and the roller.

Fig. 7 is a front view showing a contact force applied to a roller.

Fig. 8 is an enlarged view of the reduction gear of fig. 1.

Fig. 9 is a sectional view of a conventional reduction gear transmission.

Fig. 10 is a front view of the output plate and balls of the reduction gear of fig. 9.

Fig. 11 is an enlarged view of the reduction gear of fig. 9.

Detailed Description

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

As shown in fig. 1, a reduction gear 1 as a power transmission device according to an embodiment of the present invention mainly includes an input rotating portion 2, an output rotating portion 3, a roller 4 as a rolling element, a fixing member 5, and a housing 6 accommodating these members. In the illustrated example, the housing 6 includes a first housing member 6a provided on an input side (left side in fig. 1) and a second housing member 6b provided on an output side (right side in fig. 1). The

housing members

6a and 6b are fixed by an appropriate mechanism such as a bolt 23. The input rotating section 2 and the output rotating section 3 are coaxially arranged and have a common rotation center X. The fixing member 5 is fixed to the housing 6.

The input-rotating portion 2 includes an input shaft 7, an eccentric cam portion 8, a rolling bearing 9, and an input member 10. The input shaft 7 is rotatable about the rotation center X corresponding to the housing 6. In the present embodiment, the input shaft 7 is rotatably supported with respect to the housing 6 by a plurality of rolling bearings 11, and the plurality of rolling bearings 11 are fitted between the input shaft 7 and the inner peripheral surface of the output rotating portion 3. In the illustrated example, 2 bearings 11 are provided on both sides of the eccentric cam portion 8 in the axial direction. A seal member 21 for preventing leakage of grease or oil filled in the housing 6 is provided between the outer peripheral surface of the input shaft 7 and the inner peripheral surface of the first housing member 6 a. The eccentric cam portion 8 is provided on the outer periphery of the input shaft 7, and is provided integrally with the input shaft 7 in the illustrated example. The center line O1 of the cylindrical outer peripheral surface 8a of the eccentric cam portion 8 is offset in the radial direction by the eccentric amount a from the rotation center X. The input member 10 has a substantially disk shape, and the center line of the input member 10 coincides with the center line O1 of the cylindrical outer peripheral surface 8a of the eccentric cam portion 8. A rolling bearing 9 is fitted between the cylindrical outer peripheral surface 8a of the eccentric cam portion 8 and the inner peripheral surface of the input member 10. Thereby, the input member 10 is rotatable relative to the eccentric cam portion 8.

The fixing members 5 are provided on both sides of the input member 10 in the axial direction. The fixing members 5 are ring-shaped, and in the illustrated example, both the fixing members 5 are formed of the same material and in the same shape. Each fixing member 5 is fixed to the housing 6 by an appropriate mechanism. In the illustrated example, a restricting member 24 is provided to restrict the circumferential movement of the fixing member 5 with respect to the housing 6. The regulating member 24 is fitted in key grooves provided in the inner peripheral surfaces of the

housing members

6a and 6b and the outer peripheral surfaces of the fixing members 5, and is engaged with these key grooves in the circumferential direction, thereby regulating the circumferential movement of the fixing members 5 relative to the housing 6.

The input member 10 and the fixing members 5 are arranged at a predetermined interval in the axial direction. The input member 10 is formed with a plurality of first grooves 13 that axially penetrate the input member 10. A rolling element engagement groove 16 is formed on the axially inner side (the side facing the input member 10) surface of each fixing member 5. That is, in the present embodiment, the first member having the first concave groove 13 is provided as the input member 10 in the input rotating portion 2, and the pair of second members having the rolling element engagement groove 16 is provided as the fixed member 5.

In the reduction gear 1, a roller 4 having a cylindrical outer peripheral surface is used as a rolling element for transmitting torque. In the illustrated example, a cylindrical roller having a cylindrical outer peripheral surface is used as the roller 4. The roller 4 is inserted into the first concave groove 13 of the input member 10, and both ends in the axial direction of the roller 4 are engaged with the rolling element engagement grooves 16 of the fixed member 5. The roller 4 rolls in the rolling element engagement groove 16 while rotating on its own center line.

As shown in fig. 2, the plurality of first grooves 13 provided in the input member 10 are arranged at equal intervals in the circumferential direction. The track center line L1 of the first grooves 13 is formed along a circle having a radius r and centered on the center line O1. The center of curvature of the trajectory center line L1 of the first groove 13 coincides with the cylindrical outer peripheral surface 8a of the eccentric cam portion 8 and the center line O1 of the input member 10. That is, the center of curvature of the track center line L1 (i.e., the center line O1) is offset from the rotation center X of the input rotary unit 2 by the eccentric amount a. The radial width of each first groove 13 is set to be substantially equal to (slightly larger than) the outer diameter of the roller 4, and the circumferential length of each first groove 13 is larger than the outer diameter of the roller 4. Thereby, each roller 4 is held at a predetermined radial position in the first groove 13 in a state of being movable in the circumferential direction (the direction along the track center line L1). In the illustrated example, the first grooves 13 formed in the input member 10 are provided in the same number as the rollers 4. However, the number of the first grooves 13 is not limited to this, and for example, the number may be set to be smaller than the number of the rollers 4, and the plurality of rollers 4 may be penetrated by 1 first groove 13. The track center line L1 of the first groove 13 is a track of the center line of the roller 4 when the roller 4 moves in the first groove 13.

As shown in fig. 3, the raceway center line L2 of the rolling element engagement groove 16 formed in the fixed member 5 is formed by a wave-like curve that alternately intersects at a constant pitch with respect to a reference pitch circle C having a center of curvature at the rotation center X. That is, the rolling element engagement groove 16 is formed along a wavy curve, and the distance R between the wavy curve and the rotation center X changes in an increasing and decreasing manner with respect to the reference pitch circle radius PCR. In the present embodiment, 10 convex portions whose distance R from the rotation center X is larger than the reference pitch circle radius PCR are provided on the wavy curve constituting the trajectory center line L2, and 10 concave portions whose distance R from the rotation center X is smaller than the reference pitch circle radius PCR are provided on the wavy curve constituting the trajectory center line L2. The rolling element engagement grooves 16 formed in the respective fixing members 5 have the same shape, and are arranged so that the phases of the convex portions and the concave portions coincide with each other. The center line of the orbit of the rolling element engagement groove 16 is a trajectory of the center line of the roller 4 when the roller 4 is moved along the rolling element engagement groove 16.

The rolling element engagement groove 16 has a cross-sectional shape that fits into the roller 4, and is rectangular in cross-section in the illustrated example (see fig. 1). The groove width of the rolling element engagement groove 16 is set to be substantially the same as (slightly larger than) the outer diameter of the roller 4. An axial gap is formed between the bottom surface of the rolling element engagement groove 16 and the end surface of the roller 4. Further axial movement of the roller 4 is restricted by bringing the axial end face of the roller 4 into contact with any of the bottom surfaces of the rolling element engagement grooves 16.

As shown in fig. 1, the output and rotation unit 3 includes a first output member 31 provided on one axial side (left side in the drawing) of the input member 10, a second output member 32 provided on the other axial side (right side in the drawing) of the input member 10, and a coupling member 33 for coupling the first output member 31 and the second output member 32. The first output member 31 has a cylindrical shaft portion 31a and a disk portion 31b extending radially outward from the shaft portion 31 a. The second output member 32 includes a shaft portion 32a functioning as an output shaft, and a disk portion 32b extending radially outward from the shaft portion 32 a. The shaft portion 32a of the second output member 32 has a cylindrical portion 32a1 and a lid portion 32a2 that closes the opening of the cylindrical portion 32a 1. The lid portion 32a2 is provided with a coupling portion for coupling another member to which the decelerated rotation is to be transmitted. In the illustrated example, the shaft portion 31a and the disk portion 31b of the first output member 31 are integrally formed, and the shaft portion 32a and the disk portion 32b of the second output member 32 are integrally formed.

The output rotation unit 3 is rotatable about a rotation center X with respect to the housing 6. In the present embodiment, the outer diameter end of the disk portion 31b of the first output member 31 and the outer diameter end of the disk portion 32b of the second output member 32 are coupled by the coupling member 33, whereby both the

output members

31, 32 can be rotated integrally. The output rotating portion 3 is supported to be rotatable integrally with the housing 6 by a rolling bearing 14 and a rolling bearing 15, the rolling bearing 14 being fitted between the outer peripheral surface of the shaft portion 31a of the first output member 31 and the inner peripheral surface of the fixing member 5 on one axial side, and the rolling bearing 15 being fitted between the outer peripheral surface of the shaft portion 32a of the second output member 32 and the inner peripheral surface of the fixing member 5 on the other axial side. A seal member 22 for preventing leakage of grease or oil filled in the housing 6 is provided between the outer peripheral surface of the shaft portion 32a of the second output member 32 and the inner peripheral surface of the second housing member 6 b.

The disc portion 31b of the first output member 31 and the disc portion 32b of the second output member 32 are respectively provided between the input member 10 and the fixed member 5 in the axial direction. A plurality of second grooves 17 are formed in the

disk portions

31b and 32b of the

output members

31 and 32 so as to penetrate the disk portions in the axial direction. That is, in the present embodiment, a pair of third members having the second concave grooves 17 are provided as the

output members

31 and 32 in the output rotating portion 3. As shown in fig. 4, the second grooves 17 are long holes radially extending around the rotation center X. The second grooves 17 are formed at equal intervals in the circumferential direction on the same circumference. The second grooves 17 provided in the

output members

31 and 32 are provided at the same position (i.e., at the same radial position and phase) in a plane orthogonal to the axial direction. The number of the second concave grooves 17 (i.e., the number of the rollers 4) formed in each of the

output members

31 and 32 is 11, that is, 1 more than the number (10) of the convex portions or concave portions of the wave-like curve of the track center line L2.

As shown in fig. 5, the roller 4 is movable within the range of a predetermined amount m in the radial direction with respect to the reference pitch circle C in each second groove 17. In the present embodiment, a pair of parallel flat surfaces 17a facing each other in the circumferential direction are formed on the circumferential wall of each second concave groove 17, and the circumferential interval between the flat surfaces 17a is set to be substantially equal to (slightly larger than) the outer diameter of the roller 4. Thereby, each roller 4 is held at a predetermined circumferential position in the second concave groove 17 in a state of being movable in the radial direction.

As shown in fig. 6, the input member 10 of the input rotation unit 2 and the

output members

31 and 32 of the output rotation unit 3 have a common rotation center X, and the axial centers of the two fixed members 5 are disposed at the rotation center X. The central axis O1 of the input member 10 (i.e., the center of curvature of the track center line L1 of the first groove 13) is offset from the rotational center X by an eccentric amount a. The roller 4 is inserted into the first concave groove 13 of the input member 10 and the second concave grooves 17 of the

output members

31 and 32 to project on both sides in the axial direction, and the projecting portions (both ends in the axial direction) are engaged with the rolling element engagement grooves 16 of the fixing members 5 (see fig. 1). Fig. 6 schematically illustrates the respective members.

In the reduction gear 1 of the present embodiment, since the number of the convex portions of the raceway center line L2 of the rolling element engagement groove 16 is 10 (the number of the concave portions is also 10) and the number of the rollers 4 is 11, the reduction ratio i obtained by the following equation is 1/11.

Reduction ratio i (number of rollers-number of projections)/number of rollers

When the number of the convex portions is ± 1, which is the number of rollers, and the reduction ratio i is a negative value, it indicates that the rotation direction of the output rotating portion 3 is opposite to the rotation direction of the input rotating portion 2.

The shape of the raceway center line L2 of the rolling element engagement groove 16 is set so that the rotational motion from the input rotating portion 2 to the output rotating portion 3 is decelerated and transmitted in synchronous rotation. Specifically, when the reduction ratio of the reduction gear 1 is i, the shape of the rolling element engagement groove 16 is set such that the roller 4 engaged with the first concave groove 13 engages with the rolling element engagement groove 16 to transmit torque in a state where the rotation angle of the input shaft 7 is θ and the output rotating portion 3 is the rotation angle i θ. Specifically, the shape of the rolling element engagement groove 16 is set so that the distance R between the rotation center X of the input rotating portion 2 and the output rotating portion 3 and the trajectory center line L2 of the rolling element engagement groove 16 satisfies the following expression (1).

R＝a·cos(ψ/i)+√{r2-(a·sin(ψ/i))2}···(1)

However, it is possible to use a single-layer,

r: distance between the rotation center X and the raceway center line L2 of the rolling element engagement groove 16

a: eccentricity of the center O1 of the track center line L1 of the first groove 13 with respect to the rotation center X

i: reduction ratio

Psi: rotation angle of output rotating part 3

r: radius of track center line L1 of first groove 13

Of the input member 10, the

output members

31 and 32, and the fixing members 5, at least the peripheral wall of the first concave groove 13, the peripheral wall of the second concave groove 17, and the side wall of the rolling element engagement groove 16, which are in contact with the roller 4, are preferably given surface hardness to the same extent as the surface of the roller 4 in order to reduce wear caused by a difference in surface hardness with the roller 4. For example, the surface hardness of the side walls of the first concave groove 13, the peripheral wall of the second concave groove 17, and the side walls of the rolling element engagement groove 16 is preferably set to be in the range of HRC50 to 60. Specifically, the surface hardness can be obtained by forming the input member 10, the

output members

31 and 32, and the fixed member 5 with carbon steel for machine structures such as S45C and S50C, and alloy steel for machine structures such as SCM415 and SCM420, and subjecting them to bulk heat treatment or carburizing heat treatment. Alternatively, the surface hardness can be obtained by forming each member with bearing steel such as SUJ2 and subjecting them to bulk heat treatment or high-frequency heat treatment.

Next, the operation of the reduction gear transmission 1 according to the present embodiment will be described in general terms. When the input shaft 7 of the input rotating unit 2 shown in fig. 1 is rotated, the input member 10 performs a revolving motion around the rotation center X at the runout radius a. At this time, the input member 10 is free to rotate with respect to the eccentric cam portion 8 provided on the input shaft 7, and therefore, hardly performs a rotation motion. Thereby, the relative friction amount between the first groove 13 and the roller 4 is reduced, and the transmission efficiency of the rotational torque is improved.

When the input member 10 performs the revolution motion, each roller 4 engaged with the circular first concave groove 13 moves along the rolling element engagement groove 16 formed in the fixed member 5. Specifically, when the center line O1 of the input member 10 revolves in the arrow direction from the position shown in fig. 4, as shown in fig. 7, the rollers 4 engage with the first concave grooves 13 formed in the input member 10, and a substantially upward contact force F1 acts on the rollers 4. Both ends of the roller 4 in the axial direction are engaged with the rolling element engagement grooves 16, and a contact force F2' with the roller 4 is applied to the rolling element engagement grooves 16, and a contact force F2 generated by contact with the rolling element engagement grooves 16 is applied to the roller 4. The roller 4 is moved in the circumferential direction along the rolling element engagement groove 16 by the circumferential component F2a of the contact force F2. The roller 4 engages with the second concave groove 17 of the output and rotation portion 3 in the circumferential direction, and the contact force F3' generated thereby acts as a force for rotating the output and rotation portion 3 in the same direction as the input shaft 7 (see fig. 4).

The force for rotating the output rotating portion 3 (i.e., the contact force F3' acting on the second concave groove 17 of each

output member

31, 32 from the roller 4 ≈ the circumferential component F2a of the contact force F2 received by the roller 4 from the rolling element engaging groove 16) varies depending on the contact state of the roller 4 with the wavy rolling element engaging groove 16, and therefore varies in magnitude depending on the position of each roller 4 (see fig. 4). Since the roller 4 is disposed around the rotation center X of the input rotating portion 2 and the output rotating portion 3, the force for rotating the output rotating portion 3 is distributed around the rotation center X. Specifically, the force for rotating the output rotation portion 3 is large for the rollers 4 at both upper and lower ends in contact with the vicinities of the centers of the top portions of the convex portions and the top portions of the concave portions (the portions having a large inclination angle with respect to the pitch circle centering on the rotation center X) in the wavy rolling element engagement groove 16 in the figure, and the force for rotating the output rotation portion 3 is small for the rollers 4 at both left and right ends in contact with the vicinities of the top portions of the convex portions or the top portions of the concave portions (the portions having a small inclination angle with respect to the pitch circle centering on the rotation center X) in the figure.

As described above, by using the roller 4 as the rolling element for transmitting torque, as shown in fig. 8, almost no axial load is generated between the roller 4 and each member (the input member 10, the

output members

31 and 32, and the fixed member 5). In particular, when cylindrical rollers are used as the rolling elements as in the present embodiment, the axial load between the roller 4 and each member is 0. Accordingly, the load applied to the

bearings

9 and 11 supporting the input member 10 and the

bearings

14 and 15 supporting the

output members

31 and 32 only in the radial direction can reduce the size of the bearings and thus the entire reduction gear 1, compared to the case where the loads in both the radial direction and the axial direction are applied. Further, by limiting the load applied to the bearings to the radial direction, the torque loss in the inside of the bearings is reduced, and therefore, the transmission efficiency of the rotational torque is improved.

In the reduction gear 1, the pair of fixing members 5 and the pair of

output members

31 and 32 are arranged axially symmetrically about the input member 10, the rollers 4 are inserted into the first concave groove 13 of the input member 10 and the second concave grooves 17 of the

output members

31 and 32, and both ends in the axial direction of each roller 4 are engaged with the rolling element engaging grooves 16 of both the fixing members 5. During torque transmission, a contact force F1 with the first concave groove 13 of the input member 10 acts on the center in the axial direction of the roller 4, and a contact force F3 (see fig. 7) with the second concave grooves 17 of the

output members

31 and 32 and a contact force F2 with the rolling element engagement grooves 16 of the fixed members 5 act on both sides in the axial direction of the roller 4. In this way, the contact forces F1, F2, and F3 with the respective members act on the roller 4 in an axially symmetrical manner, whereby the moment applied to the roller 4 is cancelled out, and therefore the roll 4 can be prevented from falling down and the torque can be smoothly transmitted. In particular, in the present embodiment, by inserting each roller 4 into the second concave groove 17 of the pair of

output members

31 and 32 integrated by the coupling member 33, the two positions in the axial direction of each roller 4 are always kept at the same circumferential position by the second concave grooves 17 arranged at the same phase, and therefore, the inclination of the roller 4 in the circumferential direction can be reliably prevented.

In the reduction gear 1, when a friction reducing member such as a needle bearing or a sliding bearing (for example, a sintered oil-impregnated bearing) is provided in a contact portion where the roller 4 contacts at least one of the three elements of the first concave groove 13, the rolling element engagement groove 16, and the second concave groove 17, friction loss at the contact portion is greatly reduced, and torque transmission efficiency is improved. In particular, if the friction reducing member is provided at the contact portion where the roller 4 contacts two of the three elements, the contact with the remaining one element becomes rolling contact, and therefore the effect of improving the torque transmission efficiency is improved. In the present embodiment, as shown in fig. 8, the friction reducing members 30 are provided in the outer circumferential surface of the roller 4 in the axial regions in contact with the first concave grooves 13 and in the axial regions in contact with the second concave grooves 17, respectively. The location where the friction reducing member 30 is provided is not limited to the above, and the friction reducing member 30 may be provided in a contact portion where the roller 4 contacts all of the three elements. Further, if the friction reducing member is not particularly required, the roller 4 may be brought into direct contact with all of the three elements.

In the reduction gear 1, since the contact force F2 'acting on the rolling element engagement groove 16 from the roller 4 is maintained by the fixing member 5 fixed to the housing 6, a large bearing for maintaining the contact force F2' is not required. Further, the roller 4 engages with the second concave groove 17 in the rotational direction while reciprocating in the radial direction, and thereby only the contact force F3' in the rotational direction is applied from the roller 4 to the output and rotation portion 3. By limiting the direction of the contact force F3' to the rotational direction in this way, the

bearings

14 and 15 supporting the output rotating portion 3 are reduced in size to reduce the size of the reduction gear transmission 1, and torque loss in the bearing interior is reduced to improve the torque transmission efficiency of the reduction gear transmission 1.

As described above, during torque transmission, the column portion provided between the second concave grooves 17 in the

disk portions

31b, 32b of the

output members

31, 32 is applied with the circumferential contact force F3' (see fig. 7) generated by contact with the roller 4. Therefore, the column portion provided between the second concave grooves 17 of the

disk portions

31b, 32b may be damaged by the contact force F3' received from the roller 4. In particular, if the number of second concave grooves 17 (that is, the number of rollers 4) is increased in order to increase the reduction ratio, the circumferential width of the column portion between the second concave grooves 17 becomes narrow, and therefore the possibility of damage to the column portion due to the contact force F3' with the roller 4 increases.

In this regard, in the present embodiment, as shown in fig. 4, not only the contact force F3 'between the roller 4 on the upper side of the rotation center X and the second concave groove 17 but also the contact force F3' between the roller 4 on the lower side of the rotation center X and the second concave groove 17 are exerted to contribute to torque transmission. Therefore, compared to the case where torque is transmitted only by the roller 4 located above the rotation center X, for example, the contact force F3' applied from each roller 4 to the

disk portions

31b and 32b is dispersed, and therefore the load applied to the column portions of the

disk portions

31b and 32b is reduced. In particular, in the present embodiment, by providing the pair of

output members

31, 32 on both sides of the input member 10, the contact points of the roller 4 with the

output members

31, 32 are increased, and therefore the load at each contact point can be further reduced. In the present embodiment, as described above, the surface hardness of the peripheral wall of the second concave groove 17 can be increased to HRC50 or more by selecting the material of the

disk portions

31b and 32b and heat-treating. As described above, the durability of the pillar portion between the second concave grooves 17 of the

output members

31 and 32 can be improved, or the load capacity can be improved while maintaining the durability of the pillar portion.

In this way, the rotation of the input shaft 7 input to the input rotating portion 2 is transmitted to the output rotating portion 3 via the rollers 4. At this time, by designing the raceway center line L2 of the rolling element engagement groove 16 such that the distance R between the rotation center X of the input and

output rotating portions

2 and 3 and the raceway center line L2 of the rolling element engagement groove 16 satisfies the above expression (1), the output rotating portion 3 always rotates synchronously with the input shaft 7 at a decelerated rotation speed.

The embodiments of the present invention are not limited to the above. Other embodiments of the present invention will be described below, but the description of the same points as those in the above embodiments will be omitted.

In the above embodiment, the input member 10 is rotatable with respect to the input shaft 7, but the input member 10 may be configured to rotate integrally with the input shaft 7. In the above embodiment, the configuration in which the input shaft 7 and the eccentric cam portion 8 are integrally formed is exemplified, but the present invention is not limited thereto, and the input shaft 7 and the eccentric cam portion 8 may be formed separately and the eccentric cam portion 8 may be fixed to the outer peripheral surface of the input shaft 7.

In the above embodiment, the shaft portion 31a and the disk portion 31b of the first output member 31 and the shaft portion 32a and the disk portion 32b of the second output member 32 are integrally formed, but these members may be formed separately. Further, if the first output member 31 and the second output member 32 are formed of the same material in the same shape, the manufacturing cost thereof can be reduced.

In the above embodiment, the first output member 31 and the second output member 32 are coupled by the coupling member 33, but the present invention is not limited thereto, and for example, the first output member 31 and the second output member 32 may be integrally formed or may be integrated by welding. The

output members

31 and 32 do not necessarily need to be connected to each other, and may be independently rotatable.

In the above embodiment, the case where the present invention is applied to the reduction gear 1 having the reduction ratio i of 1/11 has been exemplified, but the present invention is not limited to this, and can be suitably applied to a reduction gear having a reduction ratio of any size within the range of 1/5 to 1/50, for example. In this case, the number of the convex/concave portions of the wave-like curve of the raceway center line of the rolling element engagement groove, the number of the concave grooves of the fixing member, and the number of the rollers may be appropriately set according to the reduction gear ratio i.

In the above embodiment, the case where the first member having the first concave groove 13 is the input member 10, the second member having the rolling element engagement groove 16 having the wave shape is the fixed member 5, and the third member having the second concave groove 17 is the

output members

31 and 32 has been shown, but the present invention is not limited thereto, and the power transmission method can be arbitrarily changed by appropriately allocating the first member, the second member, and the third member to the input rotating portion, the fixed member, and the output rotating portion in accordance with the specification required by the user, the use environment, and the like.

Description of reference numerals:

1 reduction gear (power transmission device)

2 input rotary part

3 output rotating part

4 rollers

5 fixed component (second component)

6 casing

7 input shaft

8 eccentric cam part

10 input component (first component)

13 first groove

16 rolling element engaging groove

17 second groove

30 Friction reducing Member

31. 32 output member (third member)

33 connecting member

Contact force between the rollers F1 and F1' and the engaging groove of the first rolling element

Contact force between the rollers F2 and F2' and the engaging grooves of the second rolling elements

Contact force of F3 and F3' rollers and grooves

Center line of orbit of L1 first rolling element engagement groove

Center line of orbit of L2 second rolling element engagement groove

O1 center of curvature of center line of orbit of first rolling element engagement groove (center line of input member)

X inputs the rotation center of the rotation part and outputs the rotation center of the rotation part.

Claims

1. A power transmission device for transmitting rotation inputted to an input rotating portion to an output rotating portion coaxially arranged with the input rotating portion at a predetermined speed ratio,

the power transmission device includes: a plurality of rollers; a first member having a plurality of first grooves through which the plurality of rollers pass; a pair of second members provided on both sides of the first member in the axial direction and each having a rolling element engagement groove in which the plurality of rollers are engaged; and a pair of third members which are respectively disposed between the first members and the pair of second members in the axial direction and have a plurality of second grooves through which the plurality of rollers pass,

the plurality of first concave grooves are formed along a circle having a center of curvature eccentric with respect to the rotation centers of the input and output rotating portions, the rolling element engagement grooves are formed along a wavy curve that alternately intersects a pitch circle having a center of curvature at the rotation center,

any member of the first member, the pair of second members, and the pair of third members is provided to the input rotation section, and any other member of the first member, the pair of second members, and the pair of third members is provided to the output rotation section.

2. The power transmission device according to claim 1,

the first member is provided to the input rotating portion, the pair of third members is provided to the output rotating portion, and the pair of second members serves as fixing members.

3. The power transmission device according to claim 2,

the pair of third members is integrally rotatable.

4. The power transmission device according to any one of claims 1 to 3,

a friction reducing member is provided at a contact portion where the outer peripheral surface of the roller contacts at least one of the three elements, i.e., the first recessed groove of the first member, the second recessed grooves of the pair of third members, and the rolling element engaging grooves of the pair of second members.